Electrically heated transfer pipe



Filed Dec. 23, 1949 y m E e 6 r e w Y B x vi W Nw A ATTORNEYS Patented Sept. 18, 1951 ELECTRICALLY HEATED TRANSFER PIPE Foster 0. Bennett, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Application December 23, 1949, Serial No. 134,780

3 Claims.

The invention relates to transferring molten solids. It more particularly concerns an electrically heated conduit apparatus in which a molten metal may be transferred, as by siphoning or pumping, from one vessel to another.

In prior attempts to provide electrically heated conduits for conveying molten solids, particularly molten metals, in which the heating of the conduit is effected by the passage of electric current through the conduit lengthwise difficulties arise which render such procedure generally unsatisfactory. One of these is the tendency for the conduit to develop hot spots particularly where the conduit is not completely filled as may be the case often times in prolonged use during which gas may collect in the conduit. In the event that a molten metal is involved and it becomes solidified as on shutting down the conduit, the presence of occluded gas makes it difficult, if not impossible, to remelt the metal and restart flow without damage to the conduit due to overheating adjacent to gas inclusions.

A particular object of the invention is to provide an electrically heated conduit for conveying a molten solid and maintaining it at a temperature above the freezing point while in the conduit without danger of local overheating. Another object is to provide an electrically heated conduit for molten metal which may be operated for long periods of time and which may be shut down by allowing it to cool so as to freeze the molten metal in it and in which frozen metal may be remelted after freezing in the conduit Without the difliculties encountered with ordinary electrically heated pipes.

With the above and other objects in view, the invention has particular relation to certain novel features of construction, arrangement of parts,

and use an example of which is given in the specification and illustrated in the accompanying drawings, wherein:

Fig. l is a side elevation largely in section showing a general arrangement of the conduit apparatus when siphoning a molten metal from one vessel to another;

Fig. 2 is a cross section on the line 2-2 of Fig. 1;

Fig. 3 is an enlarged fragmentary view of a portion of Fig. 1;

Fig. 4 is a cross section on the line 44 of Fig. 3; and

Fig. 5 is a schematic diagram of the electric heating current circuits.

Referring to the drawing in detail, in which in the several figures like numerals refer to like parts, there is shown an inner metal pipe indicated generally by numeral I, for conveying molten metal from a vessel 2, adapted to contain a supply of a molten metal, to a receiving vessel 3 as by siphoning. The inner pipe has a midportion indicated generally by numeral 4, which may be arranged to lay slightly inclined, and two end-portions indicated generally by numerals 5 and 6, respectively, depending therefrom into the vessels 3 and 2, respectively, more or less at right angles to the axis of the mid-portion and in the same vertical plane therewith. Coaxial with the inner pipe I and spaced apart therefrom is an outer pipe, indicated generally by numeral I, which extends over the whole length of the inner pipe.

Each outer end 8 and 9, respectively, of the outer pipe I is jointed by seams, such as annular rings Ill and I I, respectively, to the outside of the inner pipe so as to close the outer ends of the annular space l2 between the inner and outer pipes.

The outer pipe 1 is provided with a Z-shaped break I3 intermediate its outer ends. The inner ends I4 and I5 on either side of the Z-shaped break I3 overlap but do not touch each other, as shown in enlarged detail in Figs. 3 and 4. Fastened to the ends I4 and I5 are terminal lugs I 6 and I 1, respectively, one on each side of the break I3, for carrying heating current to the outer pipe.

The annular space I 2 between the inner and outer pipes contains spacer elements I8 of electrically insulating but thermally conducting material as mullite balls. The spacer elements maintain concentricity of the pipes I and I and allow radiant heat to pass from the outer to the inner pipe. In order to form the bends l9 and 20 while maintaining concentricity of the inner and outer pipes, wood sawdust (not shown) may be introduced into the annulus I2 along with the spacer elements so as to fill the annular space between the inner and outer pipes, especially at the places where the bends I9 and 20 are to be formed. This filling operation can be carried out before the outer ends of the inner and outer pipes are sealed with the annular rings I0 and I I.

The outside of the outer pipe 'I has a covering of thermal insulation 2| which may extend over the mid-portion as well as around the bends and along the end-portions, as shown.

The outside of the insulating covering 2I on the end-portions is provided with metal sheaths 22 and 23, respectively, the lower ends 24 and 25 of the sheaths are sealed with annular rings 26 and 21, respectively, to the outer ends 8 and 9, respectively, of the outer pipe I. The sheaths protect the thermal insulation from the destructive action of molten metal into which the endportions usually extend in use.

The conduit may be supported as by laying it in a trough 29 mounted on supports 30 and 31. In addition, the end-portions 5 and 6 may be supported, as by hangers 32 and 33, respectively, attached to the inner pipe I, which allow the pipes to expand on becoming heated.

Electrical shunt connection is made from sheath 22 to sheath 23. This may be accomplished in various ways as by cable 34, one end of which is connected to the lug 35 on sheath 22 and the other to lug 36 on sheath 23. The resistance of I the shunt connection is made less than that of the inn-er pipe and contents. For heating, the conduit lugs I6 and H are connected to a suitable low voltage high amperage transformer 39 supplied by power line 40.

The resulting electric circuits are schematically shown in Fig. 5 wherein lugs I6 and I! are shown connected to resistances 4I and 42 which correspond in resistance to the portions of the outer pipe on each side of the break I3; the resistance 43 (connected in series with 4| and 42) corresponds to that of inner pipe I and its contained molten metal, if any; and the resistance 44 (connected in parallel with 43) corresponds to that of cable 34. With this arrangement, the current supplied by transformer 39 passes in series through resistances 4| and 42 and is divided between resistances 43' and 44 according to their relative resistances.

In operation, the transformer 39 is energized from the supply lines so as to produce a potential difference between the lugs I5 and II. This induces current flow through the outer pipe I from one end I3, for example, along the outer pipe I to the end 8, thence through sheath 22 and cable 34 to the sheath 23, thence to the end 9 and through outer pipe I to the terminal end I6. Some of the current also passes from end 8 through inner pipe I to end 9, the proportion so-passing depending, as already indicated, on the resistance of the inner pipe I relative to that of the cable 34.

Current is thus allowed to pass through the outer pipe 1 until the inner pipe I becomes heated largely by radiation from pipe I to a temperature suitable for the molten solid, e. g. metal, to be transferred. By virtue of the use of balls of mullite as the spacer elements I8, heat transfer from the outer pipe I to the inner pipe I is facilitated and rendered uniform over the length of the pipes. After the inner pipe has thus been brought to a working temperature, the molten solid to be transferred is conveyed through pipe I. As illustrative of this operation, there is shown a body 45 of a molten magnesium-base alloy, i. e. an alloy of magnesium in which the magnesium content predominates, contained in the vessel 2 in which is submerged one end of the inner pipe I. Molten metal is caused to flow from the body 45 into pipe I by producing an inert gas pressure in the space 46 as by introducing an inert gas through the pipe 47 which passes through the cover 48 of vessel 2. The molten metal thereby caused to enter pipe I from the body 45 flows through the pipe I and discharges into vessel 3. The flow of molten metal through the pipe displaces gases therefrom so that the pipe becomes filled with molten metal and thereafter may be operated as a siphon without producing gas pressure in space 46 since one end, e. g. 5 as shown, can be arranged to be on a lower level than the other.

By way of illustration rather than limitation, the following design data is submitted of one embodiment of the invention:

Conveying capacity: 1500 pounds per hour of a molten magnesium-base alloy containing at least per cent of magnesium when siphoning the metal from one vessel to another, the difference in molten metal level being about 4 feet. Inner pipe I: nominal size 1 inch, length end to end 20 feet, chromesteel type 430. Outer pipe I: nominal size 2 inches, chrome steel type 430. Spacer elements I8: mullite balls inch diameter. Voltage across terminals I 5 and I5, 8 volts. Current flow: in outer pipe I, 600 amperes; in return circuits, pipe I, 200 amperes, balance in cable 34, 400

- amperes.

In transferring an aluminum-containing molten magnesium-base alloy from an iron or steel vessel through the conduit apparatus, as in the foregoing example, I have discovered that it is not unusual for the pipe I to become wholly or partially clogged in time with metallic iron which is dissolved by the magnesium-base alloy in the vessel 2 and deposited in the pipe I. I have discovered that by maintaining the pipe I at a temperature above that of the metal as it leaves the supply vessel and traverses the pipe that all such clogging is prevented. The aluminum-containing magnesium-base alloys with which the clogging difliculty is encountered are all the conventional magnesium-base alloys containing the usual amounts of aluminum as an alloying constituent such as amounts between about 0.5 and 10 per cent of aluminum or more. I

Particular advantage of the apparatus are that it heats up rapidly and uniformly, and there is no danger of the inner pipe becoming locally overheated as is the case when all the heating current passes through it. It is feasible to shut down the apparatus with molten metal in it and allow the molten metal to freeze in the inner pipe because the pipe may be reheated thereafter suificiently to melt the frozen metal and start flow without damage to the apparatus. The apparatus may be operated for long periods of time with aluminum containing magnesium-base alloys, for example, without danger of forming clogging deposits of iron merely by keeping the inner pipe hotter than the molten magnesium alloy entering it. There is greatly reduced risk of leakage in the event of a break in the inner pipe because the inner pipe is substantially completely enclosed by the outer pipe.

While the particular apparatus herein-described is well adapted for carrying out the objects of the invention, it is to be understood that the apparatus and method of the present invention includes all such modification and changes as come within the scope of the appended claims.

I claim:

1. In an electrically heated conduit for conveying a molten solid, the combination of an inner metal pipe adapted for conveying the molten solid; an outer metal pipe coaxial with said inner pipe and spaced apart therefrom over the whole length thereof, said outer pipe having a break intermediate it ends; an electrical terminal lug on the outer pipe at each side of the break; an annular seam on adjacent outer ends of the inner and outer pipes closing the outer ends of the an nular space between them and electrically connecting the adjacent ends of the inner and outer pipes; spacer elements in the annular space between the inner and outer pipes adapted to prevent the pipe from touching each other along their length; a cover of thermal insulation on the outer pipe extending from end to end of the pipe; a metal sheath over the cover at each end thereof, each sheath being electrically connected to the end of the outer pipe adjacent thereto; and electrical conductor means externally of the covering connectin one sheath with the other, said conductor means having a lower resistance than the inner pipe.

2. In an electrically heated conduit for conveying a molten solid from one vessel to another, the combination of an inner metal pipe adapted for conveying the molten solid; an outer metal pipe coaxial with the said inner pipe and spaced apart therefrom over the length thereof, said outer pipe having a break intermediate its ends; an electrical terminal lug on the outer pipe at each side of the break; an annular seam on adjacent outer ends of the inner and outer pipes closing the outer outer ends of the annular space between them and electrically connecting the adjacent ends of the inner and outer pipes; mullite ball in the annular space between the inner and outer pipe, said balls having a diameter slightly less than the width of the said annular space; a cover of thermal insulation on the outer pipe extending from end to end of the pipe, said inner and outer pipes having a substantially straight and horizontal midportion and depending end portion in the same vertical plane; a metal sheath over the thermal insulation at each end of the covering, each metal sheath being electrically connected to the end of the outer pipe adjacent thereto; and an electrical conductor means externally of the coverin connecting one sheath with the other, said conductor means having a lower resistance than the inner pipe.

3. In an electrically heated conduit for conveying a molten solid from one vessel to another, th c b n t o a ner metal p e adapted for conveying the molten solid; an outer metal pipe coaxial with the said inner pipe and spaced apart therefrom over the length thereof, said outer pipe having a break intermediate its ends; an electrical terminal lug on the outer pipe at each side of the break; an annular seam on adjacent outer ends of the inner and outer pipes closing the outer ends of the annular space between them and electrically connecting the adjacent ends of the inner and outer pipes; mullite balls in the annular space between the inner and outer pipe, said balls having a diameter slightly less than the width of the said annular space; a cover of thermal insulation on the outer pipe extending from end'to end of the pipe, said inner and outer pipes having a substantially straight and horizontal mid-portion and depending endportions in the same vertical plane; a metal sheath over the thermal insulation at each end of the covering, each metal sheath being electrically connected to the end of the outer pipe adjacent thereto; an electrical conductor means externally of the covering connectin one sheath with the other, said conductor mean having a lower resistance than the inner pipe; and a trough under the mid-portion adapted to support the same.

FOSTER C. BENNETT.

REFERENCES CITED The following references are of record in the idle of this patent:

UNITED STATES PATENTS Number Name Date 780,716 Gates Jan. 24, 1905 1,068,643 Franklin July 29, 1913 1,889,604 Jones Nov. 29, 1932 1,944,733 Doerschuk et a1. Jan. 23, 1934 1,980,825 Rankin Nov. 13, 1934 2,117,913 Seil May 17, 1938 2,191,337 Clark Feb. 20, 1940 2,397,512 Schwartz et a1. Apr. 2, 1946 2,489,753 Cox Nov. 29, 1949 

